Visual display devices

ABSTRACT

A display device comprises a plurality of gas-filled discharge devices arranged in a two-coordinate array. The discharge devices are formed in a plurality of cavities in a block, one end of each cavity being filled with an electrically resistive material and the remainder being filled with gas. Two sets of conductors are formed on the opposite surfaces of the block to enable any selected discharge device to be activated by the energization of the appropriate pair of coordinate conductors.

United States Patent [56] References Cited UNITED STATES PATENTS 3,206,638 9/1965 Moore 315/169 X 3,264,074 8/1966 Jones 315/169 X 3,3 34,269 8/1967 LHeureux 315/169 X Primary Examiner-Raymond F. Hossfeld Attorney-Cameron, Kerkam & Sutton ABSTRACT: A display device comprises a plurality of gasfilled discharge devices arranged in a two-coordinate array. The discharge devices are formed in a plurality of cavities in a block, one end of each cavity being filled with an electrically resistive material and the remainder being filled with gas. Two sets of conductors are formed on the opposite surfaces of the block to enable any selected discharge device to be activated by the energization of the appropriate pair of coordinate conductors.

PATENTEB SEP 71911 3503837! sum 1 [IF 2 VISUAL DISPLAY DEVICES This invention relates to visual display devices, and in particular to such devices comprising a large array of gas-filled cold-cathode discharge tubes each of which may be struck or extinguished to produce a visual display of the required form.

Visual display devices are known in which a plurality of gasfilled cold-cathode discharge tubes are arranged in the rows and columns of a rectangular coordinate matrix with one electrode of each tube in a row connected to an associated row conductor and the other electrode of each tube in a column connected through a resistor to an associated column conductor. A selected one of the tubes may be struck or extinguished by the variation of the potentials applied to the row conductor and column conductor which uniquely define the selected tube.

Display devices of this type using discrete discharge tubes are necessarily bulky, and attempts have been made to reduce the size of such an array. To this end, arrays of discharge tubes have been produced in which each discharge tube is formed by a cavity in a glass or ceramic block. One set of conductors is formed on the surface of a further block which is subsequently sealed to the block containing the cavities. Each such conductor is usually a transparent evaporated layer of a suitable material. The other set of conductors is not produced in the same manner since it is necessary to provide a series resistance for each discharge tube, and this is done externally.

The separate resistance necessary for each discharge tube also has a limiting effect on the size of the array, since each resistor has to be connected separately. Hence large arrays having rows and columns each containing about 1,000 discharge tubes present considerable problems.

It is an object of the invention to provide a visual display device comprising an array of gas-filled cold-cathode discharge tubes in which the problems associated with the provision of external resistors are avoided.

According to the present invention there is provided a visual display device of the type comprising a plurality of gasfilled discharge devices arranged in a two-coordinate array, which includes a block of material containing a plurality of cavities, at least the surface of the block including the surfaces of the cavities being electrically insulating, an electrically resistive material filling one end of each cavity, said material having a coefficient of thermal expansion substantially equal to that of the block, a gas filling the remainder of each cavity, a first set of electrical conductors each interconnecting one end of each cavity associated with a particular value of one coordinate, and a second set of electrical conductors each interconnecting the other end of each cavity associated with a particular value of the other coordinate.

Also according to the invention there is provided a visual display device as described in the preceding paragraph in which the block containing the cavities is formed in two parts each having a like pattern of cavities, all the cavities in one part being filled with the electrically resistive material and said two parts being sealed together with the cavities in register to form the block.

An embodiment of the invention will now be described with reference to the accompanying drawings, in which:

FIG. I shows an exploded" perspective view of part of a display device; and

FIG. 2 is a sectional elevation view of part of an assembled display device.

The drawings show a rectangular coordinate matrix of 25 discharge tubes, and are not to scale.

Referring now to FIGS. 1 and 2, the display device is built up from four glass blocks 10, 11, 12 and 13 arranged in a stack. The two middle blocks 1 1 and 12 have a matrix of small holes 14 and 15 of circular cross section formed through them in an array of rows and columns. The underside of the upper block 10 carries a number of parallel transparent evaporated conductors 16 of stannic oxide, positioned so as to pass over the tops of the holes 14 in the block 11. Each conductor 16 passes over all the holes 14 in one row of the array. The matrix is intended to be viewed from the top as seen in FIG. 1, and it is for this reason that the conductors 16 are transparent.

The holes 15 in the block 12 are filled with an electronically conducting glass of the necessary resistivity, which will be in the range 10 to 2X10 ohm-centimeters. The coefficient of thermal expansion of the resistive material should also be sub stantially the same as that of the glass block 12. Two types of glass satisfy these requirements. One is a glass based on vanadium pentoxide, having this as its major constituent. A particular form which has been found to be satisfactory has the composition, in mole percent, of 60 percent V 0 30 percent ZnO and 10 percent B 0 Another form has the composition 73 percent V 0 20 percent P 0 and 7 percent F6 0,. The other suitable type of glass is a glass-ceramic comprising a mixture of lead borosilicate and thallium oxide. Ionically conducting glasses are not suitable since they tend to dissociate.

The resistive material is preferably in powder form initially, and is placed in the holes 15 in the block 12 and subsequently fused. Hence the material must have a melting point lower than that of the block 12.

In order to provide a suitable electrode surface 19 at the interface between the material and the gas, the upper ends of the cylinders 18 of resistive material are first given an evaporated coating of a nickel-chromium alloy, and are then plated with a metal such as chromium.

The underside of the block 12 has formed on it a number of parallel conductors 17, passing over the lower ends of the cylinders of resistive material. These conductors 17, which need not be transparent, are arranged so that each one passes over all the holes 15 in one column of the array.

The lowest glass block 13 acts as a protective layer for the conductors 17, and also helps to seal the device.

When the display device is assembled the individual appertures 14 are not completely sealed off from one another, and access is provided to one or more of the apertures for evacuation and gas filling purposes. The display device is assembled by sealing the four glass blocks together around the edges, as at 20 in FIG. 2 by means of a suitable enamel, with the cavities in blocks 11 and 12 in register. The gas spaces are then evacuated and filled with a suitable gas at the required pressure, say a neon-argon mixture at about 300 torr, and then sealed off. External connections are made to the conductors 16 and 17. By way of example only, a display device may comprise up to 10 discharge tubes of about 0.02 to 0.03 inches diameter.

The display device is operated in the usual manner. The application of a suitable potential difference between a selected row" conductor and a selected column" conductor will cause the discharge tube-resistor combination located at the intersection of the two conductors to be activated, and the discharge tube will strike. Control of a large matrix may be effected in the manner described and claimed in the commonly owned copending application Ser. No. 789,476 of George Richard Hoffman filed Jan. 7, 1969.

The values of the cylindrical resistors formed in the apertures 15 may be reduced by grinding or polishing the upper surface of the block 12.

The above description and the accompanying drawings illustrate only one embodiment of the invention, and many of the features mentioned may be changed. For example, ceramic materials may be used for the blocks 10 to 13. Alternatively, the block may be made of metal with an insulating layer formed over the surfaces of the cavities and the block. The upper conductors 16 need not be transparent as stated above. It is possible to use a thin conductor, say a wire 0.002 to 0.003 inches, may be used, and this will not obscure the ends of the apertures. Alternatively, the conductors may be opaque and have holes in them in positions corresponding to the apertures 14. In this case a sufficient area of the conductor must protrude into the apertures to form electrodes. Materials such as nickel or gold may be used for the conductors.

The matrix of discharge tubes described above is of rectangular coordinate form. Any other required two-coordinate matrix may be used, for example, a matrix may have polar coordinates.

The two sets of apertures 14 and 15 in the two blocks 11 and 12 may in fact be a single set of apertures in one block, partly filled with resistive material. However, this construction introduces problems with regard to the formation of the electrodes on the upper surfaces of the resistors.

What 1 claim is:

l. A visual display device of the type comprising a plurality of gas-filled discharge devices arranged in a two-coordinate array, which includes a block of material containing a plurality of cavities, at least the surface of the block including the surfaces of the cavities being electrically insulating, an electrically resistive material located wholly within each cavity at and filling one end thereof, said material having a coefficient of thermal expansion substantially equal to that of the block and a resistivity in the range from to 2 X 10 ohm-centimeters, a gas filling the remainder of each cavity, means for sealing said cavities against the escape of gas therefrom, a first set of electrical conductors each interconnecting one end of each cavity associated with a particular value of one coordinate, and a second set of electrical conductors each interconnecting the other end of each cavity associated with a particular value of the other coordinate.

2. A display device as claimed in claim 1 in which the block containing the cavities is made from an electrically insulating material.

3. A display device as claimed in claim 1 in which the block containing the cavities is formed in two parts each having a like pattern of cavities, all the cavities in one part being filled with the electrically resistive material and said two parts being sealed together with the cavities in register to form the block.

4. A display device as claimed in claim 1 in which an electrode surface is formed in each cavity at the interface between the electrically resistive material and the gas.

5. A display device as claimed in claim 4 in which the electrode surface comprises a layer of a nickel-chromium alloy covered with a layer of chromium.

6. A display device as claimed in claim 1 in which the electrically resistive material is an electronically conducting glass.

7. A display device as claimed in claim 6 in which the glass has vanadium pentoxide as a major constituent in terms of mole percentage.

8. A display device as claimed in claim 6 in which the glass has the composition 60 mole percent vanadium pentoxide, 30 mole percent zinc oxide and 10 mole .percent boric oxide.

9. A display device as claimed in claim 6 in which the glass has the composition 75 mole percent vanadium pentoxide, 20 mole percent phosphorous pentoxide and 7 mole percent ferric oxide.

l0.-A display device as claimed in claim 6 in which the glass comprises a lead borosilicate-thallium oxide mixture. 

1. A visual display device of the type comprising a plurality of gas-filled discharge devices arranged in a two-coordinate array, which includes a block of material containing a plurality of cavities, at least the surface of the block including the surfaces of the cavities being electrically insulating, an electrically resistive material located wholly within each cavity at and filling one end thereof, said material having a coefficient of thermal expansion substantially equal to that of the block and a resistivity in the range from 104 to 2 X 105 ohm-centimeters, a gas filling the remainder of each cavity, means for sealing said cavities against the escape of gas therefrom, a first set of electrical conductors each interconnecting one end of each cavity associated with a particular value of one coordinate, and a second set of electrical conductors each interconnecting the other end of each cavity associated with a particular value of the other coordinate.
 2. A display device as claimed in claim 1 in which the block containing the cavities is made from an electrically insulating material.
 3. A display device as claimed in claim 1 in which the block containing the cavities is formed in two parts each having a like pattern of cavities, all the cavities in one part being filled with the electrically resistive material and said two parts being sealed together with the cavities in register to form the block.
 4. A display device as claimed in claim 1 in which an electrode surface is formed in each cavity at the interface between the electrically resistive material and the gas.
 5. A display device as claimed in claim 4 in which the electrode surface comprises a layer of a nickel-chromium alloy covered with a layer of chromium.
 6. A display device as claimed in claim 1 in which the electrically resistive material is an electronically conducting glass.
 7. A display device as claimed in claim 6 in which the glass has vanadium pentoxide as a major constituent in terms of mole percentage.
 8. A display device as claimed in claim 6 in which the glass has the composition 60 mole percent vanadium pentoxide, 30 mole percent zinc oxide and 10 mole percent boric oxide.
 9. A display device as claimed in claim 6 in which the glass has the composition 75 mole percent vanadium pentoxide, 20 mole percent phosphorous pentoxide and 7 mole percent ferric oxide.
 10. A display device as claimed in claim 6 in which the glass comprises a lead borosilicate-thallium oxide mixture. 